The prognosis of acute myeloid leukemia (AML) is still very poor. Thus, understanding the mechanisms regulating the biology of AML is important for developing effective therapies for this disease. Non-random chromosomal abnormalities are identified in 50-55% of all AML patients. In contrast, about 45-50% of all AML cases are cytogenetically normal (CN-AML). Recent work has identified novel recurrent gene mutations in CN- AML. Among them, mutations of the nucleophosmin (NPM1) gene, represent the most common genetic alteration in CN-AML. Recently a novel class of noncoding RNAs (transcripts longer than 200 nucleotides) named long noncoding RNAs (lncRNAs) was discovered. While lncRNAs contribute to carcinogenesis in solid tumors, their role in AML has not been characterized. Our group recently identified the lncRNA HOXB-AS3 among the top up-regulated lncRNAs in NPM1 mutated (NPM1mut) CN-AML cases. We further showed that HOXB-AS3 knockdown leads to a decrease blast proliferation and colony formation in AML cell lines and primary AML patients in vitro. Silencing HOXB-AS3 in vivo using locked nucleic acid (LNA) gapmers resulted in an increased survival of treated patient derived xenograft (PDX) mice with respect to controls. Comparative proteomics identified several RNA binding protein partners of HOXB-AS3, such as EBP1, which are associated with ribosomal biogenesis. Further experiments indicated that HOXB-AS3 binds to EBP1 and regulates ribosomal biogenesis in AML by affecting the interactions between EBP1 and NPM1 complex. Altogether, our preliminary data supports our hypothesis that HOXB-AS3 plays an important role in NPM1mut AML, and blocking HOXB-AS3 may be a viable therapeutic target in NPM1mut AML. The overall goal of this is proposal is to dissect the mechanisms through which HOXB-AS3 contributes to myeloid leukemogenesis and to explore how to target therapeutically this lncRNA. We will accomplish this goal through the following Specific Aims (SA): 1) Specific Aim 1: To elucidate the mechanisms by which HOXB-AS3 promotes leukemogenesis in AML. We will perform in vitro and in vivo studies to elucidate how HOXB-AS3 modulates cell proliferation and ribosome biogenesis; 2) Specific Aim 2: To investigate in vivo the pharmacokinetic (PK), pharmacodynamics (PD) and anti-leukemic activity of a synthetic nanoparticle tagged LNA gapmer against HOXB-AS3 using PDX models of AML. In this aim we will conduct preclinical studies of synthetic Tf-NP LNA gapmer against HOXB-AS3 in PDX models of AML overexpressing HOXB-AS3 to evaluate: a) toxicity; b) plasma PK and intracellular concentrations; c) PD endpoints; d) PK/PD modeling; and e) efficacy At completion of this project, we will have an increased understanding of the role of lncRNAs in NPM1mut AML and incorporated these findings into future treatment strategies that may improve overall outcomes.